Compounded rubber stock



Patented Got. 26, 1954 2,692,871 COMPOUNDED RUBBER STOCK Alphonse Pechukas, Akron, mesne assignments, to

Ohio, assign y Columbia- Southern Chemical Corporation, Pittsburgh, 2a., a corporation of Delaware No Drawing. Application June 29, 1950,

Serial No. 171,238

6 Claims. 1

The present invention relates to a novel combination of matter suitable for use as an improved rubber reinforcing pigment and also to rubber compositions containing such pigment and to the methods of producing these materials.

It is known that silica in finely divided state having a particle size below 0.1 micron is an efiective rubber reinforcing pigment. However, one of the objections to finely divided silica when incorporated in rubber compositions resides in the fact that the compositions containing such silica cure at a very slow rate. Furthermore, the finally cured compositions often exhibit unduly low strength characteristics. In addition, rubber compositions containing finely divided silica tend to exhibit substantial heat build-up when the cured rubber composition is subjected to dynamic tension.

To a substantial degree, these objectionable characteristics of finely divided silica are avoided when the silica, contains a substantial quantity (2 to 10 percent by weight) of free water, that. is Water which is capable of being vaporized or driven ad from the pigment by heating at a temperature of 105C. for a period of 24 hours. However, the required concentration of free water is not present in most silica pigments and in any event may be. driven off during milling thus making control difiicult.v

According to the present invention, I have been able to eliminate or substantially minimizeithese undesirable characteristics of silica and to provide a novel silica rubber pigment composition and novel rubber compositions containing such silica pigment which cure rapidly and which have optimum tensile strength and which do not exhibit the undesirable heat build-up commonly observed in prior silica pigments. I have found that these undesirable strength properties and heat build-up characteristics of silica may be avoided by coating the finely divided silica with a water miscible alkylene-polyamine orby incorporating silica and the alkylene polyamine in a rubber composition. Thus, the silica may be precoated with the polyamine or uncoated silica together with ethylene diamine or other alkylene polyamine may be compounded with rubber and the various other agents compounded with rubber. v

Various alkylene polyamines are suitable for 2. the purpose. These polyamines should be water miscible and the alkylene radical usually contains up to 5 carbon atoms. Typical alkylene polyamines which have been found to be suitable are. ethylene diamine, trimethylene diamine and tetramethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine and hexamethylene diamine. Higher molecular weight alkylene polyamines may be used provided they are water miscible.

The amount. of ethylene diamine or other alkylene polyamine which is. used is capable of some variation. Normally, about 2 to 15 percent of the polyamine based upon the weight of the silica, is. found to be suitable. While some departure from this range is possible, it is normal- 1y found that excessive amounts of polyamine have an adverse effect upon the properties of the ultimate rubber composition whereas lower concentrations, of polyamine are insufiiciently effective.

The use of an alkylene polyamine as herein contemplated has been found to be advantageous in connection with the calcium oxide silica pigment which has been described and claimed in a copending application of Edward M. Allen, Serial No. 63,205, filed December 2, 1948. Such application describes a method of preparing a silica pigment by reacting finely divided precipitated calcium silicate having an average ultimate particle size as determined by the electron microscope below about 0.1 micron (normally about 0.02;? v micron as measured by the electron microscope) with an acid having an anion which n forms a water soluble calcium salt. Typical acids which may be used for this purpose include hydrOQhloric acid, nitric acid, hypoehlorous acid, hydrobromicacid, and acetic acid.

Sumcient acid is added to produce. a slurry having a pH on the. acid S de, usually below about 4. Thereafter, the pH of the slurry is normally adjusted above 7, normally to about 7 to 8, and the precipitated silica is recovered by decantation and filtration and is dried in an oven at tempe tures of 1 G o 14 C- The water'content of this product normally is above 4. percent byweight, frequently being as much as 15 to 2.0 percent o t total w t f the product. ,Such a pigment contains a substantial quanti y, usua ly Wit the range of?! 3 to 10 percent by weight of the pigment of free water as previously defined. The balance of the water present is in the form of bound water which is the amount of water driven off from a silica pigment of the type herein described by heating the pigment at ignition temperature, for example, 1000 to 1200 C. until no further water can be removed, minus the amount of free water in the pigment. Bound water which is present in concentrations of about 2 to percent by weight of the pigment, appears to be in chemical combination with the silica.

The resultant silica also contains small amounts of calcium or like alkaline earth metal, depending upon the nature of the silicate used in its production and in general, the alkaline earth metal content, computed as alkaline earth metal oxide normally is present in a range of about to 3 percent by weight of the total pigment. On the anhydrous basis, it will be understood that this range is somewhat higher. Thus the alkaline earth metal oxide content of the silica, computed on the anhydrous pigment ranges from about to 5 percent by weight. The following are typical analyses of silica pigments which may be prepared according to the above mentioned application:

Loss on s 1 N Siol 0 0 0 Cl d amp e O. 7 11111111111 an a 2 an Percent iron oxide) 00 t ercen Ihe following is a complete analysis of a silica pigment of the type contemplated which is supplied to the trade on a commercial scale:

5.0 grams sample 95 ml. E20 2 drops saturated KCl solution.

Percentages in the above tables are by Weight.

As pointed out in the above mentioned application, the presence of the free water in the silica materially increases the rate of cure of rubber compositions in which the silica is incorporated and also increases the tensile and other strengths of the rubber composition. Hence, where the free water content is high, the use of an alkylene polyamine in conjunction with the silica in a rubber composition is not as necessary although improved results are obtained whenthe alkylene polyamine is used in such cases. Where the free water content is low or substantially absent, very poor results are obtained unless the alkylene polyamine is used.

The rubber compositions herein contemplated may be prepared simply by milling silica, alkylene polyamine, rubber and rubber vulcanization agents and other conventional compounding agents together in a conventional manner and vulcanizing the resulting product. Concentrations ranging from 5 to 100 volumes of silica per hundred volumes of rubber are found to be suitable. The term rubber as herein contemplated, is intended to include natural rubber and the conventional synthetic rubbers such as butadiene-styrene copolymers known as GR-S rubber which are copolymers of 10 to 60 percent by weight of styrene and to 40 percent by weight of butadiene, butadiene-acrylonitrile copolymers derived by copolymerization of 40 to 90 percent by Weight of butadiene, 60 to 10 percent of acrylonitrile, neoprene rubber, isobutylene polymers and copolymers of isobutylene with 0.01 to 4.0 percent by weight of isoprene (based upon the weight of isobutylene) or other elastomers prepared by polymerization of butadiene-1,3, isoprene, piperyline, 2,3-dimethyl butadiene, 2- chlorobutadiene1,3 or other comparable polymerizable compound alone or in admixture with one or more organic, monomeric or ethylenic compounds including acrylonitrile, isobutylene, vinyl chloride, vinyl acetate, styrene, methyl methacrylate, methyl alphachloro acrylate, methyl acrylate and the like. Y

According to a further embodiment of this invention, the silica may be precoated with the alkylene polyamine prior to its incorporation in a rubber composition. This may be effected, for example, by spraying the dry pulverulent silica with an alkylene polyamine while tumbling the silica or otherwise agitating it to an extent necessary in order to insure through mixing of the alkylene polyamine with the silica. Such precoating ofiers certain definite advantages. In the first place, it permits preparation of a standardized product which may be added to conventional rubber compounds without the necessity for adjustment of the rubber recipe by a rubber compounder during the rubber compounding. Furthermore the alkylene polyamine becomes more thoroughly associated with the silica and thus is more effective in combating the disadvantageous properties of the silica than would be the case where the polyamine simply is added to the rubber compound.

The invention will be more fully understood by reference to the following illustrative examples:

EXAMPLE I below the output capacity of the pump. In consequence, the solutions were subjected to turbulent intermixing in the pump.

The slurry of calcium silicate thusproduced was introduced into a tank and sufficient-hyple at 105 .Tetramethyl thiuram disulfide drochloric acid solution, containing 28% by weight of HCl was added, with stirring, to reduce the pH of the slurry to 2. 'I'hereupon, sufficient sodium hydroxide solution containing 40% by weight of NaOH was added to raise the pH of the slurry to 7.5. The precipitated silica was recovered by decantation and filtration and Was dried in an oven at an oven temperature of 120 to 140 C. for 12 hours. The free water content of the product was within the range of 3 to 8 percent by weight of the pigment.

Finely divided silica thus prepared, was dried at 105 C. for 24. hours in order to remove all of the free water. This material was ground in a micropulverizer and was placed in an oven at 105 C. for 48 hours. The finely divided silica thus obtained was placed in a conditioning room at a temperature of 25 C. and a relative humidity of 50%. Samples were removed from the conditioning room, the moisture content of each sample measured by drying a portion of the sam- C. for 24 hours and measuring the loss of free water as defined, and each sample was compounded in a rubber composition according to the following formula:

Parts by weight GR-s 100 Zinc oxide 5 Sulfur 3 Phenyl-beta-naphthylamine 1 Benzothiazyl disulfide 1.20 0.15 15.00 4.0 58.5

Paracoumarone-indene resin Ethylene diamine I-- Silica pigment The rubber compounds so prepared were vulcanized according to standard accepted procedure and the vulcanized rubber products thus {obtained were subjected to tests according to standard accepted methods of testing well established in the rubber art in order to determine the tensile strength, the tear strength and the optimum rate of cure of the rubber compounds obtained from each of the samples produced.

The results of the tests are set forth in the following table:

Table I Tensile, Pounds Square Free Moisture Content Percent by Weight (based on initial pigment) :"tion of the ethylene ber compositions according to the following formula:

Parts by weight GR-S 100.0 Zinc oxide l 5.0 Sulfur 3.0 Phenyl-beta-naphthylamine 1.0 Benzothiazy1 disulfide 1.2 Tetramethyl thiuram disulfide 0.15 Paracoumarone-indene resin 15.0 Silica pigment 58.5

These rubber compounds were tested for tensile and tear strength according to standard accepted methods normally used in testing such compositions and the following results were obtained:

Tiable II Free Moisture Content Cure at Tensile, Iear, Pounds giss y g 0 F., Pounds per per Inch ment) p g Minutes Square Inch Thickness 0.5 180 Undercured Undercured.

do Do.

It will be noted that the above tests clearly illustrate the advantageous effect of the addidiamine. Thus in Table I, it 'is shown that using 4.0 parts byweight of ethylene diamine a satisfactorily cured product was obtained within 20 to 30 minutes even when the free water content of the product was as low as 0.5 percent. In constrast, when no ethylene diamine was used, as shown in Table II (samples .containing as much as 5.5 percent by weight of free water produced uncured rubber compositions even after 120 minutes. Thus it will be seen that the presence of the ethylene diamine greatly increased the rate of cure in this case.

Similar results are obtained when trimethylene diamine and the other alkylene polyamines set forth in column 2 are used in lieu of the ethylene diamine.

EXAMPLE II GR-S 100.0 Zinc oxide 5.0 Sulfur 3.0 Phenyl-beta-naphthylamine 1.0 Benzothiazyl disulfide 1.2 Tetramethyl thiuram disulfide 0.15 Paracoumarone-indene resin 15.0

Ethylene diamine As shown Finely divided silica prepared as in Example I is mixed with 3.5 parts by weight (based upon the weight of the pigment) of ethylene diamine. This coated product is milled with the rubber composition set forth in Example I, omitting the ethylene diamine from the recipe. Results com- .parable to those set forth in Example I are obtained.

It will be understood that the rubber compositions herein contemplated may contain numerous components in addition to silica and rubber. Thus, as shown in the examples, the composition will contain the usual vulcanizing compositions including accelerators, plasticizers, carbon black and other pigments, etc. In dealing with GR-S rubber, it has been found advantageous to incorporate to 20 parts by weight of a coumarone -indene resin, preferably a coumarone resin having a melting point of about 100 0.

Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as such limitations are included in the accompanying claims.

I claim:

1. A method of preparing a rubber composition which comprises mixing rubber, a precipitated silica prepared by reaction of finely divided alkaline earth metal silicate with an acid which 0 timum Percent Duxometer Ethylene we at Modulus Tensile ar diamine 28%;, 300% p. s. 1. g fi ggfif LbsJln.

None 180 240 680 780 42 Y 2.0 20 1,820 2, 410 330 68 EXAMPLE III forms a water soluble alkaline earth metal salt,

and adjusting the pH of the medium to 7 to 8, and 2 to 15 per cent by weight of a water miscible alkylene polyamine, based upon the weight of the silica, and vulcanizing the mixture.

2. The process of claim 1 wherein the polyamine is ethylene diamine.

3. The process of claim 1 wherein the polyamine is trimethylene diamine.

4. The process of claim 1 wherein the polyamine is tetramethylene diamine.

5. The process of claim 1 wherein the polyamine is diethylene triamine.

6. The process of claim 1 wherein the polyamine is triethylene tetramine.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,418,976 Schidrowitz June 6, 1922 2,047,128 Park July '7, 1936 2,103,461 Hoch et al Dec. 28, 1937 2,114,123 Heuser Apr. 12, 1938 2,315,857 Howland Apr. 6, 1943 2,455,445 Baillie Dec. 7, 1948 2,578.605 Sears et a1 Dec. 11, 1951 FOREIGN PATENTS Number Country Date 368,867 Great Britain Mar. 17, 1932 

1. A METHOD OF PREPARING A RUBBER COMPOSITION WHICH COMPRISES MIXING RUBBER, A PRECIPITATED SILICA PREPARED BY REACTION OF FINELY DIVIDED ALKALINE EARTH METAL SILICATE WITH AN ACID WHICH FORMS A WATER SOLUBLE ALKALINE EARTH METAL SALT, AND ADJUSTING THE PH OF THE MEDIUM TO 7 TO 8, AND 2 TO 15 PER CENT BY WEIGHT OF A WEIGHT OF A WATER MISCIBLE ALKYLENE POLYAMINE, BASED UPON THE WEIGHT OF THE SILICA, AND VULCANIZING THE MIXTURE. 